The technical field involving the cutting of graphic areas from sheets, or otherwise doing narrow-path processing about graphics images on sheets, includes, for example, the face-cutting of laminate sheets to form decals. More specifically, a graphic-image area on the face layer of a laminate needs to be cut away from the remainder of the face layer so that the graphic area (e.g., a decal) can subsequently be pulled away from the backing layer of the laminate and be applied elsewhere as intended. Extremely accurate face-layer cutting about the graphics is obviously highly desirable.
This is but one example in which highly accurate sheet cutting is desirable. In many other situations, highly accurate sheet cutting may not involve face-cutting, but through-cutting, in which the full thickness of the sheet is cut about a graphics area on the sheet. And in many situations, rather than highly accurate cutting, highly accurate scoring, creasing, line-embossing or the like is desired, and in each case, of course, such processing is along a line the varying direction of which is determined by the shape of the graphics area. Together, cutting and these other types of operations on sheets having one or more graphics areas thereon are referred to herein for convenience as “narrow-path processing.” For convenience, the prior art problems and the invention herein which solves such problems will be discussed primarily with reference to sheet-cutting methods and apparatus, but such discussion is not intended to limit the scope of the invention but merely to be exemplary.
Methods of cutting and associated apparatus which address many of the problems encountered in such processing of sheet material are part of the i-cut® vision cutting system from i-cut, Inc. (formerly Mikkelsen Graphic Engineering) of Lake Geneva, Wis., and are the subject of several patents, including for the U.S. Pat. Nos. 6,772,661, 6,619,167, 6,619,168, 6,672,187, 7,140,283 and 7,040,204. The invention described in U.S. Pat. No. 6,772,661 is a method and apparatus for achieving highly improved accuracy in cutting around graphics areas in order to fully compensate for all types of two-dimensional distortion in the sheets from which the graphics areas will be cut, including distortion of differing degrees in one dimension or along one direction on the sheet of material or distortion which varies non-uniformly across the sheet. The distortion may be from the printing process or from some other post-printing process such as material handling or during the cutting process itself. This invention also provides improved speed and accuracy in cutting or other narrow-path processing and greater efficiency of material usage.
The inventions described in U.S. Pat. Nos. 6,619,167, 6,619,168 and 6,672,187 relate to improvements in the cut-processing of sheets in flatbed plotters, including methods and apparatus to speed up processing and to automate the processing of multiple sheets. In particular, U.S. Pat. Nos. 6,619,168 and 6,672,187 include a search feature which enables the apparatus to search for the first two registration marks or other reference features (e.g., corners of the sheet, elements in a graphics area, or other objects for which a position can be unambiguously determined) if one or both of these registration marks or other reference features is not where it is expected to be on the work surface.
In some cases, such as in the i-cut® system, a flatbed plotter is used. These are devices having a position-controlled cutting implement above a flat work surface on which the sheet to be cut rests. The cutting implements are controlled with controller-supplied instructions and specific graphics data based on the X-Y coordinates necessary to achieve cutting along the intended path, such as about the perimeter of a graphics area.
Despite significant advances such as those in the i-cut® system, computer-controlled cutting and other processing of graphics sheets have not yet achieved the highest levels of efficiency and performance which potentially can be reached by such automated systems. Achieving greater speed, overall efficiencies and accurate performance in cutting or other forms of narrow-path processing are continuing challenges encountered with such systems. Increased efficiency of multiple-sheet processing would be achieved if the time to “read” a group of registration marks can be reduced while at the same time maintaining a desired level of accuracy. The present invention provides improvement in such processing by reducing the total time required to “read” (sense) registration marks.